The long-term objective of this proposal is to investigate the influence of higher-level processes, such as attention, on the development of hearing. Specifically, two experiments are proposed to determine infant performance on a measure of recent interest in the adult psychoacoustic literature termed "informational masking". In contrast to "energetic" masking that results from masker energy falling within the same auditory filter as the signal, informational masking is produced by stimulus uncertainty. The mechanisms underlying informational masking are believed to be central in origin and are likely influenced by both listening experience and central maturity. Thus, determining age differences in informational masking has the potential to provide insight into the mechanisms underlying informational masking in adults. In addition, studying informational masking in infants offers an opportunity to advance our understanding of the influence of central processes on hearing during development. In Experiment 1, the influence of procedural modifications needed to study informational masking in infants will be examined. In Experiment 2, patterns of informational masking from infants and adults will be compared. The results of these experiments will inform the process of measuring and understanding informational masking in both infants and adults.